OK, I give up, I have tolerated my 2 speed long enough and I am finally going to deviate from factory specs. Who has the contacts and parts list to stuff a 3 speed auto into this? This is my daily driver, even in the rain, snow, sleet and hail, and a 3 speed auto would sure improve things, I think.
I am getting ready to pull the engine for some internal mods/upgrades, so now is as good a time as any for a trans upgrade.

Sorry. I didn't notice the Sprint mension. I always assume six with the Falcons.

You'll need the V8 stuff of course. Try to find a C4 from a V8 car. They had extra clutch plates and can take more abuse. You'll need to find a five bolt V8 bellhousing. That will be the hard part. Start searching eBay now.